The present invention relates to under oil fault sensing devices of the type used to trip a vacuum fault interrupter or circuit breaker for interrupting the primary circuit of a distribution system. Curie temperature responsive magnetic devices have been used in transformers to interrupt the primary circuit as described in U.S. Pat. No. 4,435,690 issued on Mar. 6, 1984, entitled "Primary Circuit Breaker." In this patent, a Curie temperature responsive device is described wherein a magnet is mounted on a bell crank for pivotal movement into engagement with a metallic thermal sensing element. The bell crank is biased to move the magnet away from the metal element whenever the temperature of the metal element reaches the Curie temperature allowing the magnet to release from the metal element. The pivotal movement of the bell crank is used to trip the circuit breaker. The magnet will be released from the element in response to both long-time fault currents and short-time overload fault currents. However, under high-fault currents the metallic thermal sensing element is often damaged due to the time required to heat the metal element to the Curie temperature.